Extruded, tiered high fin density heat sinks and method of manufacture

ABSTRACT

An extruded, tiered high fin density heat sink (10) uses extruded first base, second base and bridging elements (12, 16, 14) having an arrangement of closely spaced, parallel fins (20, 26, 32, 38) and recesses (22, 28, 34, 40) for receiving opposing fins in the elements. The fins (20, 38) in the first and second base elements (12, 16) are bonded to recesses (28, 34) in opposite common faces (24, 30) of bridging elements (14) while fins (26, 32) extending from both opposing faces (24, 30) of bridging element (14) are bonded in aligned recesses (22, 40) in the first and second base element (12, 16) forming an extruded, tiered, high fin density heat sink (10).

FIELD OF THE INVENTION

The invention relates to heat sinks, more particularly, the inventionconcerns extruded, bonded tiered heat sinks having a high fin density,which enables superior thermal performance in a limited space.

BACKGROUND OF THE INVENTION

Existing high performance heat sinks are characterized by a high findensity design, i.e., a fin population about twice that which can benormally produced in a standard production process. In this case, thesurface area has a major influence on the overall heat transfercapability of the heat sink. Additionally for existing heat sinks havingtightly spaced fins, the heat transfer coefficient is determined by thehydraulic diameter of the heat sink design. Hydraulic diameter isgenerally defined in the art as four times the area of the channel(i.e., space or distance between adjacent fins) divided by the perimeterof the channel. Thus, the smaller the hydraulic diameter, the higherboth the heat transfer coefficient and the heat transfer of the heatsink.

One such design is illustrated in U.S. Pat. No. 4,777,560 by Herrell etal in which a high performance, high fin density heat sink is described.According to Herrell et al., various alternative heat sink constructiontechniques are described that produce high fin density design. Aninherent disadvantage of the design is the inability to maximize thesurface area of each individual fin. Approximately 25% to 33% of thepotential individual fin surface area is not available, as this area isin contact with the adjacent fin (See for instance Herrell et al, FIGS.1, 2, 3 and 4). In addition, heat sinks based on FIGS. 1 and 2 inHerrell et al have an internal plenum that further decreases availablesurface area for a given volume of a heat sink design. Thus, Herrell etal do not teach maximizing heat sink surface area, for a given heat sinkvolume.

In U.S. Pat. No. 5,304,846 to Azar et al, a heat sink design isdisclosed that maximizes fin surface area in a high performance, highfin density heat sink. According to Azar et al., the manufacturingtechniques disclosed are crystal-orientation-dependent etching,precision sawing, electric discharge machining, or numericallycontrolled machining. A major shortcoming of the Azar et. al. heat sinkdesign is that they are generally difficult to manufacture.Additionally, the Azar et. al. heat sink requires enormously highproduction cycle time to manufacture which, of course, makes them costineffective.

In U.S. Pat. No. 4,884,331 by Hinshaw, a method of manufacturing apin-finned heat sink from an extrusion is described. According to thecross cut machine method disclosed in Hinshaw, the maximum pin findensity that can be achieved is limited to what is obtainable by anextrusion process. This latter limitation clearly would not beacceptable in the heat sink design of the present invention. Anothershortcoming of Hinshaw is that only square or rectangular pin fins canbe manufactured, no round or elliptical profiles are available.

Moreover, there exists various heat sink manufacturers that offer bondedfin heat sink assemblies in which each fin in the assembly isindividually bonded into a heat sink base. (See for instance, cataloguematerial on Augmented surface Bonded Heat Sinks published by AAVID™Thermal Technologies, Inc. (March 1996). A major shortcoming, however ofthe AAVID™ heat sinks is there enormously high cost. This cost isrelated directly to the labor required to individually arrange each finon some sort of support or substrate and high production cycle time.

Commonly owned U.S. patent applications Ser. Nos. 08/959,692, filed Oct.29, 1997 and D.76,236, hereby incorporated herein by reference, disclosecost effective techniques, based upon dual extruded or dual cast heatsinks, to manufacture high fin density heat sinks. In brief, upper andlower heat sink elements described in these patent applications arecombined together, with the lower fins being bonded into the upperrecesses and the upper fins being bonded to the lower recesses. In thesecases, due to the extrusion and die cast tooling limitations, the finheight to thickness ratio typically cannot exceed 10:1 for tightlypacked fins. High fin density heat sink applications that require tallerfins cannot be met with this dual extruded and bonded technique.

Therefore, a need persists for a high performance, high fin density,extruded, tiered heat sink with a high fin to thickness ratio, thatmaximizes heat sink surface area and is cost effective and simple tomanufacture.

SUMMARY OF THE INVENTION

It is, therefore, an object of the invention to provide an extruded,heat sink which has a high fin density and a plurality of fluid flowchannels defined by narrow passageways between nearest adjacent fins intiered elements.

Yet another object of the invention is to provide a method ofmanufacturing an extruded, tiered heat sink with bonded elementsenabling greater structural integrity.

Still another object of the invention is to provide a method ofmanufacturing a high performance, high fin density heat sink that iscost effective.

Yet another object of the invention is to provide a tiered heat sinkthat provides a plurality of integral ducts or fluid flow channels thatinsures that all air flow from a heat generating body goes through theheat sink with no air bypass.

Still further it is another object of the invention to provide multiplemounting locations for the attachment of heat generating sources.

To overcome one of more problems in the prior art, there is provided, inone aspect of the invention, an extruded, tiered high fin density heatsink which includes an extruded first base element having a plurality ofparallel first fins extending outwardly from a common first face withnearest adjacent first fins having a first recess formed therebetween inthe common first face. Also included in the heat sink of the inventionis an extruded second base element having a plurality of parallel secondfins extending outwardly from a common second face with nearest adjacentsecond fins having a second recess formed therebetween in the commonsecond face.

In addition to extruded first and second base elements, the heat sink ofthe invention includes an extruded bridging element having a thirdcommon face and an opposing fourth common face. According to ourinvention, third common face has a plurality of parallel third finsextending outwardly from the third common face with nearest adjacentthird fins having a third recess formed therebetween in the common thirdface. Likewise, fourth common face of the bridging element has aplurality of parallel fourth fins extending outwardly from the fourthcommon face with nearest adjacent fourth fins having a fourth recessformed in the common fourth face.

In a preferred embodiment of the invention, the bridging element isarranged between the first and second base elements in a manner suchthat an end edge portion of each of the first fins is fixedly bonded inan opposing third recess in the bridging element. Further, an end edgeportion of each of the third fins is fixedly bonded in an opposing firstrecess of the first base element thereby forming a plurality of fluidpassageways between the first and third fins. Moreover, an end edgeportion of each of the second fins of the second base elements is fixedin a fourth recess of the bridging element. To securely join the twoelements, an end edge portion of each of the fourth fins of the bridgingelement is fixedly bonded in a second recess of the second base elementthereby forming a plurality of fluid passageways between nearestadjacent second and fourth fins.

In another aspect of the invention, a method of manufacturing anextruded, tiered high fin density heat sink includes the steps of:providing an extrusion die for extruding metallic billets into a firstbase element, a second base element and a bridging element: and,extruding the first base element, the second base element and thebridging element, each as described above. Each of the extruded elementsare sized to a predetermined dimension depending on the desiredapplication. The common first face of the first base element is alignedwith the common third face of the bridging element so that each one ofthe first fins is properly aligned for direct insertion into a thirdrecess and each one of the third fins is aligned for direct insertioninto a first recess of the first base element. In a similar manner, thecommon second face of the second base element is aligned with the commonfourth face of the bridging element so that each one of the second finsis aligned for direct insertion into a fourth recess of the bridgingelement and each one of said fourth fins is aligned for direct insertioninto a second recess of the second base element. A bonding layer orresin is then applied to end edge portions the fins and the fins arepressed into their respective recesses as indicated above, therebyforming an extruded heat sink having gas passageways defined by spacingbetween nearest adjacent bonded fins in the first base element (definingone tier) and bridging element as well as between nearest adjacentbonded fins in the second base element and the bridging element(defining another tier).

It is, therefore, an advantageous effect of the invention that a highthermally efficient heat sink formed by extruding and bonding togetherthe first base, second base and bridge elements is cost effective andefficiently manufactured. Also the heat sink of the invention has theadded advantage of having increased structural integrity and thereforeis adaptable to more applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing as well as other objects, features and advantages of thisinvention will become more apparent from the appended Figures, whereinlike reference numerals denote like elements, and wherein:

FIGS. 1 and 2 are exploded schematic views of the heat sink of theinvention illustrating the three extruded elements from differentorientations;

FIG. 3 is a front view of heat sink elements showing the fins andrecessed channels that are used to position and bond the fins into theopposed element;

FIG. 4 is a front view of heat sink elements showing an alternativeembodiment of FIG. 3 where the bridge element has lateral endsprotruding for supporting independent elements.

FIGS. 5 and 6 are exploded schematic views (from different orientations)of the heat sink manufactured in accordance with the steps of theinvention illustrating the three extruded elements with chamferedrecesses and chamfered fin tips, to assist guiding the elements duringassembly;

FIG. 7 is a front view of the heat sink elements showing the fins andchamfered recess channels that are used to position and bond the finsinto the opposed element;

FIG. 8 is a front view of an alternative heat sink embodimentmanufactured using the steps of the invention having some fins that abutthe opposing faces of the opposing elements;

FIGS. 9 and 10 are exploded perspective views (from differentorientations) of a heat sink made in accordance with the steps of theinvention having cross cut second and third fins;

FIGS. 11 and 12 are exploded views (from different orientations)illustrating only the plurality of first and fourth fins being cross cutand air flow shields formed by the two outermost of the plurality ofsecond and fourth fins; and,

FIG. 13 is a front view of the heat sink elements shown in FIGS. 9-12.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, and more particular to FIGS. 1-7, there isillustrated the extruded, high fin density heat sink 10 manufactured inaccordance with the principles of the invention. More particularly, heatsink 10 includes extruded first and second base elements 12, 16 andbridging element 14. As best seen in FIG. 1, extruded first base element12 has a common first face 18 that accommodates a plurality ofvertically extending, substantially parallel, spaced first fins 20.Between nearest adjacent spaced first fins 20 is formed a first recesschannel 22 which extends lengthwise between the adjacent first fins 20.

Similarly, as best seen in FIG. 2, extruded bridge element 14 includes acommon third face 24 that accommodates a plurality of verticallyextending, substantially parallel, spaced third fins 26. Further, one ofa plurality of similar third recesses 28 is formed in the common thirdface 24 between adjacent third fins 26.

Similarly, as best seen in FIG. 1, extruded bridging element 14 includesa common fourth face 30 opposite common third face 24. Common fourthface 30 has a plurality of vertically extending, substantially parallel,spaced fourth fins 32. Moreover, a plurality of similar fourth recesses34 is formed in the common fourth face 30 between adjacent fourth fins32.

Depicted in FIG. 2, common second face 36 of second base element 16arranged opposite common fourth face 30 of bridging element 14 has aplurality of vertically extending, substantially parallel, spaced secondfins 38. Between nearest adjacent spaced second fins 38 is formed asecond recess 40 in the common second face 36 which extends betweenadjacent second fins 38. Skilled artisans will appreciate that multipleor partial bridging elements may be used to construct a heat sink havinga desired number of tiers.

Illustrated in FIG. 3, one tier 41 of heat sink 10 has a plurality offluid flow passageways 42 formed between nearest adjacent first andthird fins 20, 26 in the bonded first base element 12 and the bridgingelements 14. Likewise, another tier 43 of heat sink 10 has a pluralityof fluid flow passageways 42 formed between nearest adjacent second andfourth fins 38, 32 in the bonded second base element 16 and bridgingelement 14 of heat sink 10. Fluid flow passageways 42 in both tiers 41,43 enable fluid, such as heat from a heat generating body (not shown) topass through the heat sink 10 during thermal cooling.

According to another embodiment of the invention, a method ofmanufacturing an extruded high fin density heat sink 10, as describedabove, includes the step of providing an extrusion die (not shown) forextruding billets for forming first and second base 12, 16 and bridgingelement 14. We prefer using a hot extrusion process using typicaloperating conditions, i.e., temperature and pressure, corresponding tothe stock or materials being extruded. Billets formed during theextrusion process are then transformed during successive steps(described below) into a first base element 12, a second base element 16and a bridging element 14.

First and second base elements 12, 16 and bridging element 14 may beextruded from a variety of commercially available thermally conductivenonferrous stock or materials, for instance, zinc alloys, copper, copperalloys, magnesium, aluminum, and a mixture thereof. For instance, thefollowing are approximate temperature ranges for some stock materialsthat may be used in the method of the invention: aluminum, 1000-1100degrees F.; copper, 1200-2000 degrees F. In our preferred embodiment weused copper alloys which has the advantage of high thermal conductivity.

Typically, extrusion dies of the type used to form first and second baseelements 12, 16 and bridging element 14 are made of hardened H-13 toolsteel. The shape and size of the base elements, as described, are wireelectro discharge machining cut into the die. Detailed features of thefirst and second base elements 12, 16 and bridging element 14 are sizedin accordance with known shrinkage parameters and with an angular reliefcut into the backside of the die to facilitate the extrusion process.The extrusion die is configured, along with a back-up die, to fit into aconventional extrusion press of suitable tonnage for the size and weightof the base element. Thus, preferably heat sink 10 having generallyfirst and second base elements 12, 16 and bridging element 14 with aplurality of substantially parallel first, second, third and fourth fins20, 38, 26, 32 (as discussed above) extending from a respective commonface 18, 36, 24, 30 is extruded by employing an extrusion die (asdescribed) and an extrusion press of suitable size and tonnage.

Important detail features of the first and second base elements 12, 16,and bridging element 14 include the thickness of the fins and spacingbetween nearest adjacent fins in each element. Also important are theplurality of spacings between nearest adjacent first and third fins 20,26 in the bonded first base element 12 and bridging element 14 and theplurality of spacings between nearest adjacent fourth and second fins32, 38 in the bonded bridging element 14 and the second base element 16.In part, this latter feature is determined by the strength of the diematerials and extrudeability of the alloy selected for extrusion. Forcommon aluminum 6061 and 6063 alloys, we prefer a ratio of fin thicknessto fin height of about 1/10 where the fin thickness is about 0.050inches (1.27 mm) at the tip or top end portion that is inserted in therecess in the opposing common face. Preferably, the spacing is about31/2 to 4 times the thickness of the fins. We have found that fins 20,26, 32, 38 should have taper for maximum produceability, about 1/5 thefin thickness at the tip per side. The practical limit for fin thicknessis about 0.050 inches at the tip.

Moreover, the first and second base elements 12, 16 and bridging element14 of heat sink 10, having our preferred dimensions and features(described above), are then extruded from the extrusion die. The firstand second base elements 12, 16 and bridging element 14 after havingbeen extruded, are then assembled in accordance with the steps of theinvention, further discussed below.

Skilled artisans will appreciate that the extrusion process (notillustrated), described in greater details below, itself is theculmination of a series of pre-planned and scheduled functions. Billetsof the alloy used for the first and second base elements 12, 16 andbridging element 14 are purchased from one of a large variety ofvendors, such as Alcan, Shawinigan, Quebec. The billets may be cut fromlonger logs of stock material or manufactured to specification, i.e., tothe proper size, by the extruders. As is well know in the art, extrusionpresses range from 50 tons to 8,000 tons. Billets can be from 2 inchesin diameter to 24 inches in diameter. Billets are preheated toapproximately 1000 deg F., depending on the material to be extruded, andthen fed into the container of the extrusion press. Prior to preheat,however, the extrusion die and back-up die are preferably preheated andplaced ahead of the container in the die ring that holds the die and thedie back-up block.

During the extrusion process (not illustrated), a ram, with dummy blockin front, advances the billet against the extrusion die. Because this isa closed container under high pressure, the hot aluminum metal will beextruded out through the die opening resulting in a length of extrusionthe shape of the preferred extrusion die.

As will be appreciated by those skilled in the art, as the extrusionemerges from the die, an operator, sometimes referred to as a puller,will grasp the end of the extrusion and exert a degree of tension on theextrusion to keep it straight as it travels down the length of the runout table (a series of graphite blocks that guide the extrusion). Thelength of the extrusion is determined by the length of the run out tableor the ratio of the volume of the extrusion to the volume of the billet.At this length, the extrusion is cut and then allowed to cool to roomtemperature on the run out table.

The ram (not shown) will stop short of the die by about 3 inchescreating a butt or unextruded billet. At this point the container andram back off from the unextruded billet which is then sheared off forfurther processing. The container is moved forward, another billet isloaded into the container and the process begins again.

Subsequently, after the lengths of extruded material are cooled, theyare transferred to a stretcher where each end is grasped and the lengthis stretched up to 3% thereby minimizing the volumetric stresses anddistortions in the extruded material. The lengths are then cut usingcutoff saws to processing size lengths that can readily be furtherprocessed, including heat treatments, or cut to intermediate or finaldimensional size.

After extruding, the first and second base elements 12, 16 and thebridging element 14 are then independently sized to a predetermineddimension to accommodate a particular application. Dimensionally sizingthe first and second base elements 12, 16 and bridging element 14elements can be accomplished with any conventional means such asgrinding, machining, etc. Once the first and second base elements 12, 16and bridging element 14 are dimensionally sized, they are thentransferred to a saw operator where a cut-off saw sizes the part to itsfinal sized length or to an intermediate sized length. If very accuratefine sized lengths are required, the intermediate sized lengths partsmay be further sized to final size length by a variety of means such asmilling, computer numerical controlled (CNC) machining, or grinding.Final sized lengths are deburred using vibratory tumbling, handdeburring or semi-automatic brush-a-lon deburring equipment.

In alternative embodiments of the method of the invention, otheradvantageous features of the heat sink 10, such as flat mountingsurfaces, slots, drilled & tapped holes, etc. manufactured by the stepsof the invention, may be incorporated by use of secondary operations,typically milling, CNC machining, turning or piercing to complete eachpart to its final specifications. These are conventional steps that canbe implemented within the contemplation of the invention.

Referring to FIGS. 9-12, prior to applying a bonding layer (describedbelow), to bond the first base element 12 to the bridging element 14 andto the second base element 16, an alternative intervening step may beinstituted. We prefer including the step of cross cutting the first andsecond base elements 12, 16 and bridging element 14 so as to form aplurality of substantially rectangular shaped first pin fins 20,rectangular shaped second pin fins 38 and rectangular shaped third andfourth pin fins 26, 32. Cross cutting is typically performed by millingor use of a keyway cutters so as to form a plurality of substantiallyrectangular fins. Cross cutting enhances the heat transfer from fins 20,26, 32, 38 into the air by breaking up the boundary layers that formalong the surface of said fins 20, 26, 32, 38.

Referring to FIGS. 1-2, the common first face 18 of the first baseelement 12 is aligned with the common third face 24 of the bridgingelement 14, while the common fourth face 30 of the bridging element 14is aligned with the common second face 36 of the second base element. Inthis way, first fins 20 of first base element 12 are aligned for beingpressed into the third recess channels 28 in opposed third bridgeelement 14, while the fourth fins 32 of bridge element 14 are alignedfor being pressed into the second recess channels 40 in opposed secondbase element 16. Likewise, each of the third fins 26 of bridge element14 is aligned with and inserted in one of the first recesses 22 of firstbase element 12 while each of the second fins 38 of second base element16 is aligned with and inserted in one of the fourth recesses 34 ofbridging element 14.

Precise alignment of the first and second base elements 12, 16 withrespect to the bridging element 14 for assembly includes locating andorienting either of the first and second base elements 12, 16 relativeto an opposed common face of the bridging element 14. In this mannerfirst and second tiers 41, 43 (described above) of heat sink 10 areformed. Skilled artisans will appreciate that alignment of the first andsecond base elements 12, 16 and bridging element 14 prior to assemblycan be accomplished through various ways, such as with dowel pins andbushings in a fixture. Moreover, those skilled in the art will furtherappreciate that alignment can be achieved through automatic or manualmanipulation of the first and second base elements 12, 16 and bridgingelement 14.

Once the first and second base elements 12, 16 and bridging element 14are aligned, as discussed above, they are bonded together with a bondinglayer 50 in FIG. 3, preferably by applying an epoxy resin to either thetop portions of fins 20, 26, 32,38 and the recess channels 22, 28, 34,40. This process may be accomplished either automatically or manuallyusing calibrated and precise dispensing devices. We prefer automaticdispensing in the interest of reduced cycle time and cost. Moreover,although any suitable bonding material may be used, we prefer using anepoxy resin having the highest thermally conductive rating availablethat sets up in a reasonable time span, such as the thermally conductiveEpoxy Adhesive made by Thermalloy, Inc..

While the thickness of the bonding layer and the application procedureis not critical to the invention, we followed the principle that it isdesirable to produce an assembly that is economical to manufacture.Thus, we preferred applying the epoxy resin only on the top end portionsor tips 52 of the fins 20, 26, 32, 38 to accommodate ease of assembly.Referring to FIG. 2, this bonding practice was followed whether it waspreferable to bond the first, second, third and fourth fins 20, 38, 26,32 in opposing recesses 28, 34, 22, 40 (as discussed above) or,alternately, to bond the fins having length (x') against a planarportion of an opposing common face, as shown in FIG. 8.

Referring again to FIG. 2, the bonding resin has a chance to dry, thefirst, second, third and fourth fins 20, 38, 26, 32 are firmly pressedinto an aligned respective first, second, third and fourth recesschannels 28, 34, 22, 40. This practice facilitates the bonding processand provides more bonding strength between the first and second baseelements 12, 16 and bridging element 14.

As the first and second base elements 12, 16 and bridging element 14 areassembled, pressure may be applied to the opposing first and second baseelements 12, 16 and bridging element 14 which would urge into precisealignment any of the first, second, third and fourth fins 20, 38, 26, 32which may not be properly aligned. This is done through theself-aligning chamfered ends 44 provided on the tip of the fins 20, 38,26, 32 and the self aligning chamfered recesses 46.

Depicted in FIG. 5, chamfered edges are preferably between 20 deg and 30deg on each side to assure ease of entry of each of the fins 20, 38, 26,32 into the opposed chamfered recesses 46. For low volume assembly theabove could be done manually with a minimum of tooling.

In FIG. 4, an alternative embodiment of the heat sink assemble 10 hasextensions or mounting platforms 54 on either end of the bridgingelement 14, in order to accommodate additional or multiple heat (orcooling) sources. For instance, one or more heat generating bodies, suchas laser diodes (not shown), may be mounted on platforms 54 in thermalcommunication with the tiered heat sink 10.

While the invention has been described with a certain degree ofparticularity, it is manifest that many changes may be made in thedetails of construction and the arrangement of components withoutdeparting from the spirit and scope of this disclosure. It is understoodthat the invention is not limited to the embodiment set forth herein forpurposes of exemplification, but is to be limited only by the scope ofthe attached claims, including the full range of equivalency to whicheach element thereof is entitled.

PARTS LIST

10 . . . assembled heat sink

12 . . . first base element

14 . . . bridging element

16 . . . second base element

18 . . . common first face of first base element 12

20 . . . first fins of first base element 12

22 . . . first recess channels in first base element 12

24 . . . common third face of bridging element 14

26 . . . third fins of bridging element 14

28 . . . third recess channels in bridging element 14

30 . . . common fourth face of bridging element 14

32 . . . fourth fins of bridging element 14

34 . . . fourth recess channels in bridging element 14

36 . . . common second face of second base element 16

38 . . . second fins in second base element 16

40 . . . second recess channels in second base element 16

41 . . . first tier of heat sink 10

42 . . . fluid flow passageways

43 . . . second tier of heat sink 10

44 . . . chamfered ends of first, second, third and fourth fins

46 . . . chamfered recess channels in common first, second, third andfourth faces

48 . . . crosscut first and fourth fins

50 . . . bonding layer

52 . . . end edge portions of fins

54 . . . extended surfaces for mounting heat sources

56 . . . butt joint

58 . . . crosscut second and third fins

60 . . . assembled heatsink

What is claimed is:
 1. A tiered high fin density heat sink, comprising:afirst extrusion of a first base element having a plurality of parallelfirst, generally rectangularly shaped fins extending outwardly from acommon first face with nearest adjacent first fins having a first,generally rectangularly shaped recess formed therebetween in said commonfirst face; a second extrusion of a second base element having aplurality of parallel second, generally rectangularly shaped finsextending outwardly from a common second face with nearest adjacentsecond fins having a second, generally rectangularly shaped recessformed therebetween in said common second face; a third extrusion of abridging element having a third common face and an opposing fourthcommon face, wherein said third common face has a plurality ofalternating first crest, each one of said alternating first crest havinga parallel third, generally rectangularly shaped fin extending outwardlyfrom said third common face with nearest adjacent third fins having athird, generally rectangularly shaped recess formed therebetween in saidcommon third face, and wherein said fourth common face has a pluralityof alternating second crest, each one of said second crest having aparallel fourth, generally rectangularly shaped fin extending outwardlyfrom said fourth common face with nearest adjacent fourth fins having afourth, generally rectangularly shaped recess formed in said commonfourth face; and, wherein said bridging element is arranged between saidfirst and second base elements in a manner such that a first end edgeportion of each of said first fins is fixedly bonded in an opposingthird recess in said bridging element and a third end edge portion ofeach of said third fins is fixedly bonded in an opposing first recess ofsaid first base element thereby forming a plurality of fluid passagewaysbetween said first and third fins, and wherein a second end edge portionof each of said second fins of said second base elements is fixed in afourth recess of said bridging element and a fourth end edge portioneach of said fourth fins of said common fourth face is fixedly bonded ina second recess of said second base element thereby forming a pluralityof fluid passageways between said second and fourth fins, and whereinsaid first, second, third, and fourth end edge portions are chamfered bybetween 20 to 30 degrees from a central point along each of said first,second, third, and fourth end edge portions.
 2. The heat sink recited inclaim 1 wherein said first and second base elements and said bridgingelement each comprises materials selected fromthe group consistingof:(a) zinc alloys; (b) copper; (c) copper alloys; (d) magnesium; (e)aluminum; and, (f) mixture thereof.
 3. The heat sink recited in claim 1wherein said first base element and second base element are bonded tosaid bringing element with a thermally conductive epoxy adhesive.
 4. Theheat sink recited in claim 1 wherein said first base element and secondbase element are fixedly bonded to said bridging element by vacuumbrazing.